First a quick review of down structure. Each individual cluster of down consists of multiple branches radiating from a central point, or quill, where the cluster attaches to the bird. These branches quickly diverge into a series of sub-branches, each of which hosts hundreds of tiny fibrils. Each of these fibrils feature an extensive array of microscopic, hook-like "nodes" along their length. These nodes enable the fibrils to interlock and create an extensive honeycomb of dead air spaces that provides its insulating ability.

This picture was taken by an electron microscope and shows a down branch magnified 120 times. Notice the many sub-branches and the tremendous number of fibrils that then radiate from them.

These next two pictures show individual fibrils magnified 950x (left) and 1,900x (right). Note the distintive nodes that line the fibrils. They come in two types: "triangle" and "crotch." These elements are what allow the thousands of individual fibrils to interlock and create the intricate 3-D structure of a down cluster.

Pretty amazing stuff. No wonder we can't create a synthetic alternative to down!

Check out the full article to learn more about the remarkable physical structure of down, including its unique chemical composition and an in-depth scientific treatment of its reaction to moisture, humidity, and compression.

About Matt Heid

I love gear, and I'm passionate about using it in the field. While doing research for several hiking guidebooks—including AMC's Best Backpacking in New England—I’ve hiked thousands of miles across New England, California, Alaska, and other wilderness destinations. I also cycle, climb, and surf. For the past five years, I’ve shared some of my experience in the “Equipped” column of AMC Outdoors. I look forward to sharing more through this blog. Happy Trails!

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